Conditioning process and device for producing pure water

ABSTRACT

The invention pertains to a process for the production of pure water, in which raw water, or feed water similarly, is fed to a treatment apparatus (1) that has at least one semi-permeable membrane (4), in conjunction with which a partial quantity of the raw water passes through the membrane (4) as pure water under the driving force of a pressure differential, and the remaining quantity of raw water that flows past the membrane leaves the treatment apparatus (1) as concentrate. In order to counteract any excessive soiling of the membrane (4), and to attain the longest possible operational and membrane service lifetimes, it is provided that the direction of flow of the raw water past the membrane (4) is reversed at intervals of time. The invention also pertains to a treatment apparatus (1) for the production of pure water, with at least one semi-permeable membrane (4). The treatment apparatus (1) has at least two apparatus openings (10, 11) that feed into its raw water, or feed water, area (5), one of which is used as a water inlet for feeding the raw, or feed water to the membrane (4), and the other is provided as a water outlet for the concentrate, and at least one pure water outlet in its pure water area (6), the treatment apparatus openings (10, 11) that lead to the raw water, or feed water area (5) are provided with a flow reversing device to at intervals of time alternately be used as a water inlet or as a water outlet.

FIELD OF THE INVENTION

The invention pertains to a process for the production of pure water, inwhich raw water, or feed water similarly, is fed to a treatmentapparatus that has at least one semi-permeable membrane, in conjunctionwith which a partial quantity of the raw water passes through themembrane as pure water under the driving force of a pressuredifferential, and the remaining quantity of raw water that flows pastthe membrane leaves the treatment apparatus as concentrate.

The invention is also concerned with a treatment apparatus for theproduction of pure water, with at least one semi-permeable membranewhich separates a raw water, or feed water, area from a pure water areain such a way that a partial quantity of the raw, or feed water thatflows past the membrane passes through the membrane as pure water underthe driving force of a pressure differential, in conjunction with whichthe treatment apparatus has at least two openings that feed into its rawwater, or feed water, area, one apparatus opening of which is used as awater inlet for feeding the raw, or feed water to the membrane, and theother apparatus opening of which is provided as a water outlet for theconcentrate, and in conjunction with which the treatment apparatusexhibits at least one pure water outlet in its pure water area.

BACKGROUND OF THE INVENTION

With ultrafiltration, microfiltration, and, in particular, the reverseosmosis technique, various procedures are already known for theproduction of pure water, in which from raw water that is charged with amixture of substances, pure water that is less charged than the rawwater is produced by means of a semi-permeable membrane.

Thus, a treatment apparatus that exhibits a so-called winding modulewithin an apparatus housing is already known. This winding module iscomprised of several double-walled flat membranes that are wound inspiral fashion around a filtrate collector pipe. While the filtratecollector pipe and the interior membrane areas, enclosed by the twowalls of each membrane, are a part of the pure water area of thepreviously known treatment apparatus, the outer walls of the flatmembranes, which overlap and are held at a slight distance, limit itsraw water area. The raw water flows into the raw water area of thewinding module at the one end, to leave this raw water area at theother, opposite end of the module as concentrate. As this is takingplace, only a partial quantity of the raw water that flows past the flatmembranes passes through them as pure water under the driving force of apressure differential.

Since the raw water flows only in one direction through the windingmodule of the previously known treatment apparatus, the winding moduleexhibits a ring seal only at the end that is facing the direction offlow--a ring seal whose sealing lips point against the direction of flowand towards the inner wall of the adjacent apparatus housing and sealoff the annular gap between the inner wall of the apparatus housing andthe outer side of the tubularly wound winding module.

As is the case with other membrane modules, a winding module of such atype is also susceptible to impurities and breakdowns. For that reason,there is routinely placed ahead of such modules, in the direction offlow, a sieve-like pre-filter, which is supposed to counteract anydirtying of the membranes by large particles and which has to be changedfrequently if the raw water is heavily contaminated. In spite of that,the membranes still get dirtied during periods of operation,particularly in the winding module end area that is facing the directionof flow of the raw water.

SUMMARY OF THE INVENTION

Therefore, the task exists particularly of creating a process for theproduction of pure water that allows longer periods of operation andgreater service intervals for the semi-permeable membranes that are usedwith it. At the same time, the task exists of creating a treatmentapparatus specifically for carrying out this process.

In the case of the process of the type described at the beginning, thesolution in accordance with the invention consists of the fact that thedirection of flow of the raw water past the membrane is reversed orchanged at intervals of time.

Through a reversal in the direction of flow of the water past themembrane or membranes, both end areas of the module being used areutilized. When this is done, the particles of dirt that had come torest, particularly in the area that was facing the direction of flowbefore the reversal of the flow direction, are rinsed out, while theopposite end area of the module, which until then had been less heavilyloaded with particles of dirt, forms the front-most area in thedirection of flow until the next reversal in the direction of flow. Bymeans of this front-and-back utilization of the module, its operationaland membrane service lifetimes can be substantially increased and thenecessary maintenance intervals lengthened. Since with each reversal inthe direction of flow, the area of the module that had been moreseverely dirtied until then temporarily forms the area that is rear-mostin the direction of flow and that is rinsed by raw water, the otherwiseusual pre-filters that are placed ahead of the module can be dispensedwith as such, which makes for a not-insignificant savings in space andexpenses.

In accordance with a further developmental suggestion that is importantenough to be deserving of protection in its own right, it is providedthat by means of a time-related reduction or interruption of thedischarge of pure water at the membrane, an increase of the static waterpressure on the pure water side of the membrane is brought about, andthat following a static increase in the pressure on the pure water side,and particularly, following a balance of the static water pressure onboth sides of the membrane, the static water pressure that exists on theraw water side of the treatment apparatus is lowered, at intervals oftime, briefly and preferably abruptly, relative to the static waterpressure that exists on the pure water side. Particularly by means ofsuch an abrupt or pulse-like reduction of the static water pressure thatexists on the raw water side of the treatment apparatus relative to thestatic water pressure that exists on the pure water side, the productionof pure water is indeed interrupted. However, this transient change inpressure leads to a surge-like reverse flow of the pure water from thepure water area, which is briefly exhibiting the higher static pressure,to the raw water area. This reverse flow brings about a thorough rinsingof the membrane walls as well as a cleaning of the module at appropriateintervals of time, so that longer membrane service periods areencouraged. In conjunction with this, by way of example the flow speed,and with it the dynamic water pressure of the raw water that is flowingpast the membrane, can be increased in order to lower the static waterpressure that exists on the raw water side.

A preferable process sequence provides that the discharge of the rawwater and the discharge of the pure water at the membrane are brieflyreduced or interrupted at intervals of time, and that before any openingor increase of the pure water discharge, an opening or increase of theraw water discharge takes place at the membrane, preferably in a flowdirection that is reversed relative to the direction of flow of the rawwater past the membrane before the reduction or interruption. If, forexample, the raw water discharge and the pure water discharge at themembrane are stopped briefly at intervals of time, at first, the samestatic pressure is built up on both sides of the membrane. If the rawwater discharge is now opened first, then, in accordance withBernoulli's equation, the static pressure on the pure water side of themembrane is facing a static water pressure on the raw water side of themembrane that is less (through an increase in the dynamic waterpressure). This transient static pressure differential, which, incomparison with the pressure differential during the pure waterproduction phase, creates opposing static pressure relationships, bringsabout a surge-like reverse flow of the pure water through the membranetowards the raw water side, which rinses out the particles of dirt thathave become lodged on the raw water side. With the subsequent opening ofthe pure water discharge as well, these pressure relationships are againremoved, and a higher relative pressure is achieved on the raw waterside, which is necessary for the production of pure water using, forexample, reverse osmosis. By means of this reversal of the direction offlow, the rear-most end area before the reversal of the direction offlow now forms the front-most end membrane area, in which the particlesof dirt lodge more severely. By means of a constant change in thepressure relationships on both sides of the membrane, as well as in theflow direction of the raw water, the treatment apparatus is continuouslycleansed of dirt particles, which encourages long operational andmembrane lifetimes.

It is beneficial if the intervals of time that are provided for areversal of the direction of flow and/or for a change in the waterpressure at the membrane, and/or the extent of the water pressure changeat the membrane are chosen depending on the degree of contamination ofthe raw water or feed water. By means of a change with respect to theduration and frequency of the time intervals provided for a reversal ofthe direction of flow and for a change in the water pressure in the purewater area and/or the raw water area, the process for the production ofpure water, in accordance with the invention, can be adapted to thedegree of contamination of the raw water that is being used. However, inaddition to, or instead of this, such an adaptation can also be broughtabout by means of an increase or a decrease of the relative staticpressure that is prevailing on the pure water side in comparison to theraw water side, if during the rinsing or cleaning phase of the treatmentapparatus, a comparatively lower relative static pressure exists on thisraw water side, and the pure water transfers through the membrane fromthe pure water side to the raw water side.

It is also possible, after every reversal of flow direction, to supplyraw water, or feed water from the same raw water source, to thetreatment apparatus. What is meant by feed water is any water that isfed into the treatment apparatus for the production of pure water. If,however, because of an increased concentration of the raw water orbecause of its high salt content, it is feared that there may be anunwanted higher osmotic counter-pressure of such a type that would makea buildup of pressure in the pure water area difficult or impossible,then it may be beneficial if pure water, or water with a lower saltcontent to be used as feed water, is temporarily fed to the treatmentapparatus for intermittent flow-through in a reverse flow direction,especially during the rinsing phase of the treatment apparatus, which isa brief reduction of the static water pressure on the raw water side incomparison with the water pressure existing on the pure water side ofthe treatment apparatus.

As a result, for a time only pure water, or water with a low saltcontent, flows past the membrane on the raw water side during one of thetwo directions of flow. Thus, fed to the membrane in the one directionof flow, and particularly during the pure water production phase, is theraw water from the feed water source in question, in conjunction withthis, and following a reversal in the direction of flow (that is, duringthe rinsing phase, in which the static water pressure existing on theraw water side is briefly lowered in comparison with the static waterpressure existing on the pure water side) to send past the membrane inthe other, opposite direction of flow, a portion of the pure water thatwas produced up to that point in time or water with a lower saltcontent.

Particularly if sieve-like pre-filters placed ahead of the treatmentapparatus in the direction of flow have been dispensed with, it can beadvantageous if chemical deposit aids, adsorption agents, and/orabsorption agents (for example, activated charcoal powder) are fed intothe raw water, or feed water, ahead of the membrane in the direction offlow.

The solution in accordance with the invention, in the case of thetreatment apparatus of the type mentioned at the beginning, consistsparticularly of the fact that the apparatus openings that lead to theraw water, or feed water, area of the treatment apparatus are providedat intervals of time alternately as a water inlet or a water outlet. Afurther development in accordance with the invention provides, inaddition, that the flow direction of the water past the membrane on theraw water, or feed water, side can be reversed by means of aflow-reversing device, whereas this flow-reversing device can be made upof multiple-way valves.

In order to be able to bring the water pressure in the raw water areaand in the pure water area to the same static water pressure, forexample, and, in conjunction with this, to be able to briefly lower thestatic water pressure in the raw water area for the surge rinsing of themembrane, it is beneficial if, for the alternating pressure matching andpressure changing of the water pressure existing in the raw water areaand in the pure water area of the treatment apparatus, the pure wateroutlet and the apparatus openings that lead to the raw water area caneach be regulated by means of a stop valve or a similar kind of shut-offdevice or regulating device. In conjunction with that, a surge-likethorough rinsing of the membrane by the water that is temporarilytransferred from the pure water area into the raw water area isencouraged if the stop valves are configured as ball valves or a similarkind of quick-acting fitting.

In order to be able to thoroughly rinse the membrane over a specificperiod of time during the rinse phase of the treatment apparatus, oneform of implementation in accordance with the invention provides that,between the pure water area of the membrane and the stop valve of thepure water outlet, there is provided an intermediate reservoir that isconnected, preferably without a check valve, with the pure water area ofthe treatment apparatus so that a larger quantity of the pure water cantransfer through the membrane into the raw water area of the treatmentapparatus when the pressure relationships are suitable.

The treatment apparatus can be operated with the most varied membranemodules when using the process in accordance with the invention. Inaccordance with one suggestion that is especially easy to produce, inaccordance with the invention, it is, however, provided that thetreatment apparatus exhibits at least one winding module as asemi-permeable membrane and that at least one face of the winding moduleserves preferably as a deposit filter and/or a pre-filter.

In conjunction with that, it can be advantageous if the treatmentapparatus has an apparatus housing for holding a winding module, thehousing interior of which is connected with the feed-side andoutlet-side raw water line, or feed water line, and if the annular gapformed between the winding module and the apparatus housing is providedwith a ring seal which is preferably placed at one end region of thewinding module and which seals the annular gap in only one direction offlow, and which is permeable in the opposite direction of flow. Since inthe case of a form of implementation such as this, the annular gap,formed between the outer housing and the winding module, is also rinsedthrough, at least in one flow direction, against the blocking directionof the ring seal for the raw water, by this raw water, an unwantedbuildup of dirt is also counteracted in this area of the treatmentapparatus.

Additional features of the invention can be found in the followingdescription of an implementation example in accordance with theinvention, in conjunction with claims and the drawing. The individualfeatures can be realized either each by itself, or in multiples, withinone form of implementation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Shown in the representation, which is heavily schematicized in parts,are the following:

FIG. 1 A treatment apparatus for the production of pure water, whichexhibits, in a pipeline or a similar apparatus housing, a winding modulethrough which raw water flows,

FIG. 2 An additional, simplified representation of the treatmentapparatus in FIG. 1, whereby the raw water flows through the treatmentapparatus in a direction that is reversed with respect to that of FIG.1,

FIG. 3 The treatment apparatus from FIGS. 1 and 2, whereby the raw waterdischarge and the pure water discharge are each shut off by means of astop valve.

FIG. 4 The treatment apparatus from FIGS. 1 through 3 in a so-calledrinsing phase, in which only the pure water discharge is shut off andthe static water pressure that exists on the pure water side is facing astatic water pressure that is lower on the raw water side, which leadsto a transfer of pure water through the membrane to the raw water sideof the treatment apparatus, and

FIG. 5 A treatment apparatus that is likewise shown in its rinse phaseand that is similar to the one in FIGS. 1 through 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 shows a treatment apparatus 1 for the production of pure water,which contains a winding module 3 inside a tubular apparatus housing 2.The winding module 3 has at least one semi-permeable membrane 4, whichis shown here in a tubular shape and indicated by means of dashed lines.The semi-permeable membrane separates a raw water area 5 from a purewater area 6 of the treatment apparatus 1.

The annular gap 7 that is formed between the outside of the windingmodule 3 and the inside of the apparatus housing 2 is sealed by means ofa ring seal 8 of the winding module 3, the outer sealing lip 9, orsimilar external free end, of which points in the direction towards theadjacent front end of the winding module 3. As a result of thisconfiguration of the ring seal 8, it seals the annular gap 7 only in thedirection of flow of the raw water that is shown in FIG. 1, while it isat least partially permeable in the opposite direction of flow of theraw water.

At each of the two ends of the winding module 3 there is provided atleast one apparatus opening 10 and 11, here ring-shaped, of which theone apparatus opening 10 in FIG. 1 is used as a water inlet forsupplying the raw water, or feed water, and the other apparatus opening11 is provided as the water outlet for the concentrate that is flowingpast the membrane 4. The pure water area 6 of the treatment apparatus 1makes a transition into the filtrate collector pipe 12, which on bothsides of the winding module 3 protrudes beyond the module and forms thepure water outlet 13 (cf. FIGS. 3 through 5).

As with the usual winding modules, in the pure water production phaseshown in FIG. 1, the raw water that is supplied to the treatmentapparatus 1 flows through the apparatus opening 10 in the arrowdirection Pf1 and into the raw water area 5. Since during the pure waterproduction phase a water pressure that is higher than that of the purewater area 6 prevails in this raw water area 5, a partial quantity ofthe raw, or feed water that is flowing past the membrane 4 passesthrough the membrane 4, under the driving force of a pressuredifferential, as pure water which can be drawn from the treatmentapparatus 1 at the left and/or right ends, as shown in FIG. 1, of thefiltrate collector pipe 12.

In the phase of pure water production that is represented in FIG. 1, thecontaminants that are contained in the raw water are collected primarilyin the front-end area, relative to the direction of flow, of the windingmodule 3, while the rear-end area, relative to the direction of flow, isless loaded with dirt particles. In order to also make use of the endarea of the winding module 3 that is presently less loaded with dirtparticles and in order to attain longer membrane service periods, theflow direction of the raw water past the membrane, in the treatmentapparatus 1, in accordance with the invention, is changed at intervalsof time.

FIG. 2 shows the treatment apparatus 1 following one such reversal ofthe flow direction in an additional simplified representation. It can beseen clearly in FIG. 2 that the flow direction of the raw water past themembrane 4 is reversed, or changed, at intervals of time. The apparatusopening 10 that is being used as a water inlet in FIG. 1 forms the wateroutlet in FIG. 2, while the apparatus opening 11 that was provided asthe water outlet, before the reversal of the flow direction, is providedas the water inlet in FIG. 2, which, since it is now the front end areaof the winding module 3 in the direction of flow Pf2, is more stronglysubject to soiling.

It can be seen in FIG. 3 that the pure water outlet and the apparatusopenings 10 and 11 that lead to the raw water area 5 can each beregulated by means of a stop valve 14 and 15. Of the stop valves thatare assigned to the apparatus openings 10 and 11, only the stop valve 14of the apparatus opening 10 is shown. By means of the closing of thestop valves 14 and 15 and the interruption of the raw water and purewater discharge at the membrane 4, approximately the same water pressureis built up on the raw water side 5 as on the pure water side 6 of thetreatment apparatus 1. In order to then, at intervals of time, abruptlyand briefly lower the static water pressure that exists on the raw waterside 5 relative to the static water pressure that exists on the purewater side 6--as is shown in FIG. 4--the raw water discharge is releasedfirst, before any opening of the pure water discharge, so that thestatic pressure that exists on the pure water side 6 is facing acomparatively lower static water pressure and the correspondingly higherdynamic water pressure on the raw water side 5. In this rinsing phase,which is shown in FIG. 4, there exists a static water pressure on theraw water side 5 that is lower in comparison with the pure water side 6of the treatment apparatus 1, for which reason pure water transfers fromthe pure water area 6 through the membrane 4 into the raw water side 5,and in doing so, rinses out the particles of dirt lying on the membrane4 on the raw water side. In conjunction with this, the static pressureof the raw water flowing past the membrane 4 can be reduced even furtherby means of an increase in the speed of the flow, and thus the dynamicwater pressure of the raw water that is being supplied to the treatmentapparatus 1 in arrow direction Pf2 (cf. FIG. 4). In FIG. 4, thisincrease in the speed of the flow of the raw water is shown by doublearrows.

To increase the cleansing effect during the rinse phase, it is alsopossible for raw water discharge to be alternately opened and closedrepeatedly while the pure water discharge is closed. As a result ofthis, a repeated, pulse-like change in pressure is brought about on bothsides of the membrane, along with the corresponding surge-like reverseflows of pure water through the membrane.

If, in conjunction with that, the stop valve 15, and thus the dischargeof pure water, is opened again, the water pressure that exists on theraw water side 5 then exceeds the water pressure that prevails on thepure water side 6 of the treatment apparatus 1, so that the treatmentapparatus 1 again makes the transition into the pure water productionphase until the next reversal of flow direction. After a certain periodof operation, a reversal of the flow direction of the raw water can becarried out again in accordance with FIGS. 1 through 4--but withreversed directions of flow.

It is beneficial if the intervals of time that are provided for areversal of the direction of flow and/or for a change of the waterpressure at the membrane 4, and/or the extent of the water pressurechange at the membrane 4, are chosen depending on the degree ofcontamination of the raw, or feed water. It can also be beneficial if,especially during the rinse phase shown in FIGS. 1 through 3, purewater, or a water with a lower salt content, is temporarily fed throughone of the apparatus openings 10 and 11 to the treatment apparatus 1 asthe raw water, which flows past the membrane in arrow direction Pf2.

The flow direction reversal, which is shown in FIG. 1 on the one handand in FIGS. 2 through 4 on the other, as well as the supplying of purewater into the raw water area 5 of the treatment apparatus 1 by means ofthe apparatus openings 10 and 11, can, for example, be carried out bymeans of appropriate multiple-way valves, which are part of aflow-reversal device.

In order to achieve an abrupt static pressure change on the raw waterside 5 with respect to the pure water side 6 of the treatment apparatus1, it is beneficial if the stop valves 14 and 15 that are assigned tothe apparatus openings 10 and 11, as well as the pure water outlet 13,are configured as ball valves, or a similar type of quick-actingfitting.

In order to be able to clean the membrane 4 as long as possible and aseffectively as possible during this rinsing phase, the treatmentapparatus 1 shown in FIG. 5 exhibits, between the pure water area 6 ofthe treatment apparatus 1 and the stop valve 15 of the pure water outlet13, an intermediate reservoir 16 which is connected without a checkvalve to the treatment apparatus' pure water area and which encourages alonger cleansing back-flow of the pure water through the pores of themembrane 4 into the raw water area 5 of the treatment apparatus 1, andwhich forms an air-chamber-like pressure cushion for increasing thereverse-rinse intensity. In conjunction with that, the rinse phaserepresented in FIGS. 4 and 5 can take place before, during, or after aflow direction reversal of the raw water past the membrane 4.

While the flows of raw water in FIGS. 1 through 5 are designated by Pf1and Pf2, the reference symbols Pf3 (pure water production phase) and Pf4(rinsing phase) are assigned to the flows of pure water.

Since the winding module 3 of the treatment apparatus 1, in accordancewith the invention, is cleaned at intervals of time by means of areversal of the flow direction of the raw water past the membrane 4 inthe raw water area 5, and by means of a brief, surge-like reverse flowof the pure water from the pure water area 6 through the membrane 4 intothe raw water area 5, a sieve-like pre-filter can be dispensed with,which makes for a not-insignificant savings of space and expense. Withthe treatment apparatus 1, coarse particles are trapped in the region ofthe apparatus openings 10 and 11, in conjunction with which the twofaces of the winding module are used as a deposit filter and apre-filter. In order to increase this cleaning effect of the apparatusopenings 10 and 11, it can be beneficial if chemical deposit aids,adsorption agents, and/or absorption agents are fed into the raw waterahead of the membrane 4 in the direction of flow, at least during one ofthe flow directions that are shown in FIG. 1 on the one hand, and inFIGS. 2 through 4 on the other. Also, an advantage of the treatmentapparatus 1, in accordance with the invention, is the fact that theannular gap formed between the winding module 3 and the apparatushousing 2 is cleaned by the raw water that flows past the winding module3 in arrow direction Pf2 (cf. FIGS. 2 through 4) and which, in this flowdirection, lifts the sealing lip 9 of the ring seal 8 from the innerside of the apparatus housing 2 and can flow past the ring seal 8.

The treatment apparatus 1, which is preferably operated using thereverse osmosis technique, is distinguished by its long operational andmembrane service lifetimes.

I claim:
 1. Process for the production of pure water, in which raw wateris fed in a first flow direction to a treatment apparatus having a rawwater side and a pure water side, comprising the steps of:passing apartial quantity of raw water through at least one semi-permeablemembrane disposed within the treatment apparatus under a driving forceof a pressure differential to obtain pure water; discharging theremaining quantity of raw water flowing past the membrane in the firstflow direction from the treatment apparatus as a concentrate; reducingthe discharge of pure water at timed intervals to increase static waterpressure on the pure water side of the membrane; following the increasein the static water pressure on the pure water side, reversing thedirection of flow of the raw water that flows past the membrane to lowerstatic water pressure that exists on the raw water side of the treatmentapparatus relative to the static water pressure on the pure water sideto reverse the flow of pure water through the membrane; and increasingpure water discharge.
 2. Process in accordance with claim 1, furthercomprising the step of increasing the speed of the raw water flowingpast the membrane in order to lower the static water pressure on the rawwater side.
 3. Process in accordance with claim 1 further comprising thesteps of:reducing the discharge of the raw water at the time thedischarge of the pure water is reduced; and before increasing the purewater discharge, increasing the raw water discharge.
 4. Process inaccordance with claim 1, further comprising the step of:choosing theextent of the water pressure change at the membrane depending on thedegree of contamination of the raw water.
 5. Process in accordance withclaim 1, further comprising the step of:temporarily feeding to thetreatment apparatus, for intermittent flow through the raw water area ina reverse flow direction, one of pure water and water with a saltcontent that is lower in comparison with the raw water.
 6. Process inaccordance with claim 1, further comprising the step of:feeding at leastone of chemical deposit aids, adsorption agents, and absorption agentsinto the raw water ahead of the membrane in the direction of flow. 7.Process in accordance with claim 1, characterized by the fact that theprocess for pure water production is a reverse osmosis process. 8.Treatment apparatus for the production of pure water comprising at leastone semi-permeable membrane which separates a raw water area of thetreatment apparatus from a pure water area such that a partial quantityof the raw water that flows past the membrane passes through themembrane as pure water under the driving force of a pressuredifferential, at least first and second apparatus openings in fluidcommunication with the raw water area, a flow reversing device in fluidcommunication with the first and second apparatus openings via conduits,the flow reversing device being adapted to direct raw water to the firstapparatus opening and to allow discharge of a concentrate from thesecond apparatus opening in a first configuration to feed raw water tothe membrane in a first flow direction, and the flow reversing devicebeing adapted to allow discharge of concentrate from the first apparatusopening and direct raw water to the second apparatus opening in a secondconfiguration to feed raw water to the membrane in a second flowdirection, at least one pure water outlet in fluid communication withthe pure water area, and a pressure control valve being located at eachof the first and second apparatus openings and the pure water outlet forregulating the flow through the apparatus openings and the pure wateroutlet for changing water pressure in the raw water and pure waterareas.
 9. Treatment apparatus in accordance with claim 8, characterizedby the fact that the valves are ball valves.
 10. Treatment apparatus inaccordance with claim 8, characterized by the fact that between the purewater area and the valve at the pure water outlet there is provided anintermediate reservoir that is fluidly connected to the pure water areaof the treatment apparatus.
 11. Treatment apparatus in accordance withclaim 8, further including at least one spiral wound module as thesemi-permeable membrane.
 12. Treatment apparatus in accordance withclaim 11, further comprising a housing having an interior for holdingthe spiral wound module, the housing interior being connected to a rawwater line, and an annular gap being located between the spiral woundmodule and the housing interior, a ring seal being located at an endregion of the spiral wound module which is adapted to seal the annulargap in only one direction of flow, and which is permeable in theopposite direction of flow.